Method of automatically controlling motor speed of gas-cutter

ABSTRACT

A method of automatically controlling the speed at which a gas flame cutter travels over the work to assure a uniform and complete cut. The flames generate a voltage between the gas nozzle and work which pulsates, the pulsation becoming greater as cutting efficiency decreases due to an excessively fast rate of travel of the nozzle. The pulsations are transformed into a signal to be fed into an electric control system to regulate the nozzle speed.

United States Patent Arata et al.

[451 Mar. 21, 1972 METHOD OF AUTOMATICALLY CONTROLLING MOTOR SPEED OF GAS-CUTTER Inventors: Yoshiaki Arata, Amagasaki; Katsunori Inoue, Ashiyashi, both of Japan lwatani & Co., Ltd., Osaka, Japan Filed: Feb. 24, 1969 Appl. No.: 801,287

Assignee:

Foreign Application Priority Data Apr. 30, 1968 Japan ..43/28899 US. Cl ..l48/9 Int. Cl

Field of Search 148/9; 266/23 [56] References Cited UNITED STATES PATENTS 2,089,014 8/1937 Bucknam et a1 148/9 2,442,013 5/1948 Mott et al. ...148/9 2,534,958 12/1950 Deming 148/9 Primary ExaminerDelbert E. Gantz Assistant Examiner-C. E. Spresser Attorney-Amold Robinson [5 7] ABSTRACT T regulate the nozzle speed.

6 Claims, 10 Drawing Figures Patented March 21, 1972 3,650,847

3 Shaw-Shunt 2 FBG.6

ouT OPUT AAllA I Ivi' INPUT INVENTOR.

ATTORNEY Patented March 21, 1972 3,650,847

3 Sheets-Shut :5

w 0 l O A'l'A'l'l'A 2 Q J m I O) -l j I N r- LIJ INVENTOR. 3 CL ATTORNEY METHOD OF AUTOMATICALLY CONTROLLINGv MOTOR SPEED OF GAS-CUTTER BACKGROUND OF THE INVENTION In industry there are many uses for gas flame cutters. They are a quick and practical means of cutting-throughzmetal. In many operations, particularly in .mass production, the gas flame nozzle is supported on a carriage and led across the work. This method isspeedy and accurate.

One disadvantage of such a method is that if the speed of the carriage is too great, nonuniform and even incomplete cutting can occur. It is, of course, desirable that:the cutting.

speed be kept as high as possible so that the cutting operation is compatible with mass production. Unfortunately, factors such as metal quality, metal thickness, the position of the metal with respect to the nozzle, gas flow, etc.,.dete'rmine how fast the nozzle can be moved over the work and still produce a satisfactory cut. Thus, the maximum nozzle speed varies so that it is possible to inadvertently exceed that speed and thereby cut poorly or incompletely so that the metal is not completely separated along the line of cut.

SUMMARY OF THE INVENTION BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of a gas flame nozzle and wiring for conductingthe pulsating voltage between nozzle-and work into a circuit suitable to perform the present method;

FIG. 2 is a graph of'the pulsative components;

FIG. 3 is a block diagram of a circuit in which the pulsative components are detected for'use in adigital system;

. FIGS. 4 and 5 are block diagrams of a circuit -inwhich the pulsative components are detected for use in an analog system;

FlG.6'is a schematic view of a smoothing circuit;

FIG. 7 is a block diagram of a control system'circuit for use in a digital system; 7

FIG. 8 is a schematic diagram of a control system circuit;

FIG. 9 is a block diagram of a control system circuitfor use with the present invention; and

FIG. 10 is a schematic diagram of a-c ontrol system useful in performing the'present method.

DETAILED DESCRIPTION OF THE DRAWINGS FIG. I shows pre-heating flames 2 jetting through a nozzle 1 and impinging against material 3 to be cut. The hot gas flames have the characteristics of wholly ionized plasma fluids. When such plasma fluids come into contact with the work of-electri cally conductive material, negatively charged electrons tend to reach the work faster than ions, thereby increasing the negative charge of the work. In this situation, if the nozzle is electrically insulated from its surroundings, it will have positive potential in relation to the work. FIG. 2 shows the simplest arrangement for detecting the electric potential thus produced between the nozzle and the work. In this way, electromotive force will begenerated while high pressure oxygen jets through the nozzle, in which, as is apparent from FIG. 2, pulsative components of the electromotive-force are functions of the varying conditions of the material being cut. ln'FIG. 2, the three lines each show a phase of the pulsative components involved in the voltage between the nozzle 1 and the work 3 and which are functions of the varying conditions of the material being cut. The uppermost line indicates that the cutting is being performed most properly. The pulsations are less appreciable than in any of the other two phases. The middl lines shows that the cutting has begun to decrease in efficiency. The pulses increase in number in comparison with those of the upper line. The lower line indicates that the cutting has become even more inefficient. The pulses have greatly increased in number.

The reason why such pulses are present in the voltage between a nozzle and the work can be explained as follows:

When cutting is proceeding efiiciently, high pressure oxygen flames go down through the cuts which are present in the material together with high temperature slugs which are produced by hot gas flames because of oxidation with iron around the cuts. When the cutting efficiency is reduced owing to unfavorable acceleration of the cutting speed, oxygen flames will not be able to go through the cuts in the material but rather, they will be detained in part around the cuts, resulting in turbulence of the pre-heating flames. This causes the electromotive force which is generated by the pre-heating flames between the nozzle and the material to violently fluctuate.

In the present invention, motor speed of a gas-cutter is controlled by transforming the pulsativecomponents into control signals in a detecting system. More concretely, the primary object of this invention is to provide a method of automaticallycontrolling motor speed or travelling speed of a gascutter through a control system, the gas-cutter being so designed as to be in gradual acceleration when there are no pulsative components kept, so that the cutting may proceed efficiently throughout the cutting process. Therefore, this necessitates that pulsative components should be quantitatively detected in a suitable form for this controlling operation, that is to say, for controlling the motor speed of the gas-cutter. FIGS. '3-6 show examples of detecting circuits.

In FIG. 3, varying pulsative components are expressed in termsof numbers of pulses in a digital system in which the voltage between nozzle and work is applied to the amplifier B is the form of input A. The DC components in the input A are eliminated and the remaining pulsative components will be amplified, simultaneously followed by the conversion of input A into impedance. At the second stage, there is a band-pass filter C having the transmission zone adjacent to a basic mode of frequency generated when the cutting decreases in efficiency. The output delivered from the band-pass filter C is generally a sinusoidal wave form of infinite frequency, but it will be trimmed with a portion below a given level blanked out by means of the subsequent level-slicer D. The Schmitt circuit E is intended to change the deformed wave form into a shape where the wave is equal in height and mode. This produces unified pulses well adapted for the input of the control circuit when delivered in the form of the output 0,.

In FIG. 4, the procedure followed is identical to that of FIG. 3 up to the level slicer D. There the output delivered from the level slicer D has its fluctuations removed through the smoothing circuit F whereby the output may be rectified almost into direct current. FIG. 6 shows and example of such a smoothing circuit F. The input delivered from the right-hand terminal is integrated through C and R into the output almost in the form of direct current. FIG. 5 shows a block diagram of a detecting circuit for an analog system, but lacks a band-pass filter C and a level slicer D like those shown in FIG. 4.

Operation of the control system circuit used for the regulation of the motor speed with the input delivered from a detecting circuit in the form of the output 0,, will now be explained with reference to both the digital and analog systems.

A digital system is shown in FIG. 7 in which, with no delivery of the input to this system, a motor control circuit H will'be actuated so as to step up the motor with accelerating signals from a circuit G where the accelerator signals are generated. On the other hand, if the input is delivered in the form of pulses from a detecting system being used with a digital system on the circuit I where decelerating signals are generated in accordance with the number of pulses, the control circuit H will be actuated so as to step down the motor. Thus, through the control of the motor, the travelling speed of the gas-cutter will be always appropriately maintained in such a manner that the speed will be accelerated with non-delivery of input to the control system, and will be decelerated in accordance with the number of pulses with the delivery ofinput to the control system.

FIG. 8 shows a circuit under this system, in which if no pulse input is delivered between T, and T a transistor T,, will be kept in the off" position and a condenser C, will be charged through a resistor R, from an electric energy source B, followed by a rise of voltage between T, and T with the timeconstants of R, and C,. This causes transistor T to raise the basic potential thereof through T, and T resulting in a reduction of resistance R between the collector and the emitter. Further, this causes a fall of the time constant (R-l-R )/C for the charging circuit, resulting in a shortened period of time required from the charge of the condenser C in synchronism with the AC source (of commercial frequency) through the transistor T, up to the ignition of SCR through a pulse transformer PT by means of a unijunction transistor UJT,so that a greater amount of current may be delivered to the DC motor to gradually step it up. On the contrary, if with the delivery of pulse input between T, and T a transistor T,, is maintained in the ON position to permit a passage of current, where the basic potential is kept positive, the condenser C, will be discharged at the terminal owing to a short circuit, resulting in a fall of the terminal voltage. This causes the basic potential of T to fall, followed by a rise of the time constant (R-l-R VC which causes a time-lag in the ignition of SCR and consequently a decrease in the current supplied to the DC motor, resulting in a reduced speed of that motor.

FIG. 9 shows a control system for use with an analog system. The input voltage is impressed almost in the form of direct current to the control system. The voltage thus impressed and the reference voltage previously set are compared in a comparator J to find the difference between them which difference, after amplification, will be supplied to the control circuit H for the motor. The control circuit H is intended to control the motor M to accelerate or decelerate it in accordance with characteristics of the difference, such as its positiveness, negativeness or magnitude.

FIG. 10 shows an example of this circuit, in which, with the input voltage E, applied to the input terminals T, and T the difference between E, and the reference voltage E will be amplified by means of a differential amplifier DA consisting essentially of T,,, T,,, T,;,, and T thus causing a rise or a fall in the basic potential of transistor T,,,. For example if E, is larger than E the basic potential will fall, resulting in an increase of resistance R between the collector and the emitter, whereas, if E, is smaller than E the basic potential will rise, resulting in a reduction of resistance R. The remaining procedure will be followed in the same way as in the case of the digital system.

Thus, as has been hitherto described, pulsative components of the electromotive force involved in hot gas flames can be electrically detected in the form of pulses under either a digital or analog system so as to control motor speed, so that the cutting efficiency may be improved. It may be accomplished by keeping the motor at constant speed when during periods of good cutting performance no response to the pulses occurs, but by stepping up the motor when with pulses becoming small owing to a possible retarded speed of cutting, or by stepping down the motor when with the pulses becoming large because ofa possible excessively accelerated speed ofcutting.

It will be apparent from the foregoing that in accordance with this invention no special means is necessary for installation adjacent to a nozzle or anywhere else in order to obtain the optimum efficiency throughout a cutting operation. All that is necessary is that the electrical insulation of the nozzle from its surroundings be enough to determine the cutting condition of the material to be processed through the detection of pulsative components in the electromotive force which is present in re-heatin as flames, so that the detected signals may be fe to contro t e travelling velocity of an automatlc gas-cutter fitted with a nozzle, resulting in an improved efficiency throughout the cutting operation.

The advantages of the present invention, as well as certain changes and modifications of the disclosed embodiments thereof, will be readily apparent to those skilled in the art. It is the applicants intention to cover all those changes and modifications which could be made to the embodiments of the invention herein chosen for the purposes of the disclosure without departing from the spirit and scope of the invention.

We claim:

1. A method of automatically controlling motor speed of a gas cutter comprising the following steps:

1. detecting pulsative components in the electromotive force generated between a gas flame-emitting nozzle and the material which forms the work as a result of the more rapid rate at which electrons reach the work as compared to positive ions in the hot gas flame;

2. transforming said pulsative components into control signals; and

3. varying the rate of speed of said nozzle relative to said work in accordance with said control signals.

2. The method according to claim 1 wherein the rate of speed of said nozzle is gradually accelerated in the absence of said pulsative components.

3. The method according to claim 1 wherein the rate of speed of said nozzle is gradually decelerated in the presence of said pulsative components.

4. The method according to claim 1 wherein said step ofdetecting said pulsative components comprises the following steps:

1. amplifying the AC component of the voltage between said nozzle and said work;

2. selecting the frequency components in the range of the basic frequency of said pulsative component to form a substantially sinusoidal wave; and

3. shaping said sinusoidal wave into pulses of constant amplitude, said pulses comprising the input to a control circuit for varying the rate of speed of said nozzle.

5. The method according to claim 1 wherein said step of detecting said pulsative components comprises the following steps:

1. amplifying the AC component of the voltage between said nozzle and said work;

2. selecting the frequency components in the range of the basic frequency of said pulsative component to form a substantially sinusoidal wave; and

3. converting said sinusoidal wave into a variable DC current output.

6. The method according to claim 1 wherein the step of transforming said pulsative components into control signals comprises the step of comparing said pulsative components with a reference voltage, and generating a control signal which varies according to the difierence between said pulsative components and said reference voltage. 

2. transforming said pulsative components into control signals; and
 2. The method according to claim 1 wherein the rate of speed of said nozzle is gradually accelerated in the absence of said pulsative components.
 2. selecting the frequency components in the range of the basic frequency of said pulsative component to form a substantially sinusoidal wave; and
 2. selecting the frequency components in the range of the basic frequency of said pulsative component to form a substantially sinusoidal wave; and
 3. converting said sinusoidal wave into a variable DC current output.
 3. shaping said sinusoidal wave into pulses of constant amplitude, said pulses comprising the input to a control circuit for varying the rate of speed of said nozzle.
 3. The method according to claim 1 wherein the rate of speed of said nozzle is gradually decelerated in the presence of said pulsative components.
 3. varying the rate of speed of said nozzle relative to said work in accordance with said control signals.
 4. The method according to claim 1 wherein said step of detecting said pulsative components comprises the following steps:
 5. The method according to claim 1 wherein said step of detecting said pulsative components comprises the following steps:
 6. The method according to claim 1 wherein the step of transforming said pulsative components into control signals comprises the step of comparing said pulsative components with a reference voltage, and generating a control signal which varies according to the difference between said pulsative components and said reference voltage. 